1. Field of the Invention
The invention relates to a projection apparatus. Particularly, the invention relates to a projection apparatus capable of improving light utilization efficiency.
2. Description of Related Art
Generally, a conventional projection apparatus includes two lens arrays and a digital micro-mirror device (DMD), wherein the lens array includes a plurality of lens cells, and the lens cells in the two lens arrays are corresponded one-by-one. A light beam is guided to the DMD by the lens units on the lens arrays, so as to achieve functions of beam shaping and light spot uniformization. However, since a shape of the DMD is a rectangle, a shape of the lens cell of the conventional technique is also required to be a rectangle, so as to produce a uniform light spot with a preferred shape on the DMD.
In the conventional projection apparatus, the lens array located closer to a light source has a specific effective light receiving angle range. After the light beam emitted from the light source enters a lens cell of the lens array located closer to the light source in an angle within the effective light receiving angle range, it is further transmitted the corresponding lens cell of the other lens array and then transmitted to the DMD. However, after the light beam enters a lens cell of the lens array located closer to the light source in an angle outside the effective light receiving angle range, it cannot be transmitted to the corresponding lens cell of the other lens array, but is transmitted to another lens cell next to the corresponding lens cell, so that a propagating direction of the light beam is deviated and the light beam cannot reach the DMD, which may cause a light loss, which is a so-called crosstalk phenomenon, and brightness interference causes the light loss.
Since the effective light receiving angle range of each of the lens cell is related to a width of the lens cell, when the light beam passes through the lens cell, an effective light receiving angle of the light at a short side of the lens cell is smaller than an effective light receiving angle of the light at a long side of the lens cell. Therefore, when an incident angle of the light beam incident to the lens cell is greater than the effective light receiving angle of the lens cell, the propagating direction of the light beam is deviated from the DMD, which may cause loss of light utilization efficiency. Since a currently popular display image is developed towards a trend of 16:9 widescreen, a length-width ratio of the lens unit of the DMD used by the conventional projection apparatus is also 16:9. Therefore, the short side of the lens cell is liable to be excessively short, so that the effective light receiving angle along a direction parallel to the short side is excessively small, which may cause more loss of light.
Taiwan Patent No. I300834 discloses a lighting system including a point light source array, a lens and a collimating lens, wherein the collimating lens is disposed between the point light source array and the lens. Moreover, Taiwan Patent No. I324237 discloses a lens cell having a body, a light incident surface, a light emitting surface, a divergent part, and a convergent part.